All participants will use portion-controlled foods to replace 2 meals per day during the first 6 months of treatment and to replace 1 meal per day during months 7 to 18. Participants will purchase their own portion-controlled foods, although in-kind contributions from private industry will be sought to offset participants' food costs. The study consent form will explicitly describe estimated food costs for study participants. The cost of the meal plan, a "partial meal replacement" diet (replacement of 2 out of 3 meals per day) is not expected to increase food costs. Many participants should observe a decrease in food costs while following the meal plan.